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Study of the QCD Phase Structure through High Energy Heavy Ion Collisions

Bedanga MohantyNational Institute of Science Education and Research

(NISER)

Outline: QCD Phase Structure Theoretical and Experimental status Highlights from RHIC Beam Energy Scan Program Summary

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Phase Diagram and Basic Interactions

Phase diagram of Water Electromagnetic interactionPrecisely known

Phase diagram of strong interactionsLargely still a conjecture

arXiv:1111.5475 [hep-ph]

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QCD Phase Diagram

Rich phase structure:-- Phases QGP & Hadronic-- Cross over-- 1st order-- Critical Point

Physical systems undergo phase transitions when external parameters such as the temperature (T) or a chemical potential (μ) are varied.

Conserved Quantities: Baryon Number ~ Electric Charge ~ Q ~ small Strangeness ~ S ~ small

K. Rajagopal and F. Wilczek, Handbook of QCD

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QCD Phase Diagram - Experimental

Vary beam energy to change Temperature & Baryon Chemical Potential

Vary: T, B, S, Q

Conservation in strong interactions-- Charge -- Baryon number-- Strangeness

Nature 448 (2007) 302

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Transition Temperature

Nucl. Phys. A 830 (2009) 805c

Prog. Theor. Phys. Suppl. 153, 106 (2004)

gparton ~ 47 ~ g (2/30)

g ~ 3

High Temperature De-confined state of quarks and gluons

Science 332 (2011) 1525-1528

Phys.Rev. D85 (2012) 054503

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Cross-over Nature443:675-678,2006

No significant volume dependence

At high T and = 0 is a cross over.

JHEP 1208 (2012) 053

Phys. Rev. Lett. 110, 012302 (2013)

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Establishing Quark Gluon Phase

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initial > c (Lattice)

At and below 11.5 GeV – Hadronic interactions dominate. Need pA data for a quantitative statement.

QGP turned off ?

STAR: QM2012

Eur.Phys.J. C72 (2012) 1945; Advances in High Energy Physics 2013

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Establishing Quark Gluon Phase

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Partonic Collectivity De-confinementTurned off at low energy ?

STAR Preliminary

Phys. Rev. Lett., 110, 142301 (2013)

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Establishing Quark Gluon Phase

At and below 11.5 GeV – Hadronic interactions dominate.

QM2012: STAR

o Possible Local Parity Violation effectso Requires De-confined matter of quarks and gluonso Requires chiral symmetry to be restored

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QCD Phase structure at B ~ 0 Close to zero baryonic chemical potential the

QCD transition corresponding to a state of de-confined quarks and gluons takes place at high temperature.

First principle QCD calculations suggest it is a cross over. Indirectly supported by experimental data.

Transition temperature using chiral condensates ~ 154 MeV, using Susceptibilities and Polyakov loop ~ 175 MeV – width around 15 MeV

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Transition Line - Theory

Width of transition line wide Freeze-out line close to transition line at Lower B

Larger B deviations of freeze-out curve from transition line Interesting T vs. B dependence at lower beam energies

JHEP 1104 (2011) 001

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Softening of Equation of State

Minimum between 11-20 GeV Softening of Equation of State ?

STAR Preliminary

Theory:D. H. Rischke et al., Heavy Ion Phys. 1, 309 (1995).H. Stoecker, Nucl. Phys. A 750, 121 (2005).J. Brachmann et al., Phys. Rev. C 61, 024909 (2000).L. P. Csernai and D. Rohrich, Phys. Lett. B 458, 454 (1999).

)(tan

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x

y

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rn nv

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QCD Phase structure at B > T Transition line from lattice QCD has large

uncertainties.

Transition line close to chemical freeze-out line at small B but deviates at large B. Interesting trends of T vs. B at lower energies.

Experimental hints towards no QCD transition to de-confined state ~ 11.5 GeV center of mass energy.

Directed flow data shows non-monotonic dependence on beam energy – Soft EOS ?

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Search for Critical Point - Theory

Numerical QCD calculations difficult at large B – sign problem

Techniques: Reweighting, Taylor expansion & imaginary potential

Issues (not common to all) : lattice spacing, physical quark mass, continuum limit, Volume

Theory still some more work to be done …… need more CPU

S. Gupta, QM2009 Acta Phys.Polon.Supp. 5 (2012) 825-835Phys. Rev. D 78, 14503 (2008);

JHEP 0404, 50 (2004)Phys.Rev.D71:114014,2005

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Search for Critical Point - Experiment

Nuclear liquid-gas transition with a critical end point

Beam Energy Scan Program at RHIC

Observables : Related to correlation length or susceptibility

< (N)2> ~ 2 < (N)3> ~ 4.5 < (N)4> - 3 < (N)2>2 ~ 7

Challenging to measure :Finite size effects < 6 fmCritical slowing down, finite time effects ~ 2 - 3 fm

No dynamical theoretical estimates exists. Experimentally look for non-monotonic variations with beam energy (T, B).

S ~

Phys.Lett. B696 (2011) 459Phys.Rev.Lett. 105 (2010) 022302

Phys. Rev. Lett. 102, 032301 (2009)Phys. Rev. Lett. 91, 102003 (2003)Phys. Rev. D 61, 105017 (2000)

Phys.Rev.Lett. 107 (2011) 052301

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Search for Critical Point - Experiment

STAR: arXiv: 1309.5681 (submitted to PRL)Phys.Rev.Lett. 105 (2010) 022302

Central collisions Deviations from PoissonianDeviations from transport modelDeviations from peripheral collisions Higher statistics needed at 7.7 & 11.5 GeV + a new data point around ~15 GeV

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More on Net-proton Higher Moments

Below 27 GeV results dominated by protons only

Anti-protons follow Poisson

Protons deviate from Poisson

Net-protons deviate from Poisson

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More on Net-proton Higher Moments

Comparison with Hadron Resonance Gas Model with exact acceptance.

Deviations from HRG model observed

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QCD Phase structure: Critical Point

Science 332 (2011) 1525-1528

Theory: Lattice QCD calculations have uncertainties. Some calculations indicate it to lie between 10-30 GeV beam energy

Experiment: If signal survives hadronization then ruled out for beam energies > 39 GeV

Promising prospects below 39 GeV. High statistics data set needed below 20 GeV.

Theory+Experiment: Need quantitative dynamical theory calculations with realistic correlation lengths to compare to data.

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Rich Physics from RHIC - BES

No Jet quenching

Jet quenching

Softening of EOS

Critical point search

NCQ Scaling

No NCQ Scaling

NCQ Scaling

No NCQ Scaling

CME

No CME

Caveat: Qualitative picture

STAR Preliminary

STAR Preliminary

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Experimentally accessible by colliding Heavy-Ions at different beam energies

QGP

Hadron Gas

Lattice QCD and experiments suggest there are two distinct phasesBeam Energy Scan Program – hints at turn-off of QGP signatures

QGP

Hadron Gas

154 – 175MeV

Cross-over

At~ 0 : Lattice QCD: Transition temperature and cross-overSupported by experimental data

QGP

Hadron Gas

154 – 175MeV

Cross-over

First order

At> T: Lattice QCD and Models : CP and transition line(model uncertainties needs to be controlled)Experimental data very intriguing : proton v1 and fluctuations

SummaryWhat is known about the QCD phase diagram and to what degree ?

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Phase structure: Interesting Possibilities

Quarkyonic phase (Theoretical) Experimental signature (Baryon correlations, Photons) ?

Rept.Prog.Phys. 74 (2011) 014001

Nucl.Phys. A830 (2009) 709C-712CNucl. Phys. A 796, 83 (2007 arXiv:1302.1119